Interpretive Summary: Production of edible vaccines in plants could have a tremendous impact on human health. Once vaccine-containing plants have been developed, vaccines can be produced and delivered with lower costs and technology requirements than conventional vaccines. Furthermore, most people prefer medications that can be taken orally to those which are administered by injection. The beneficiaries of this technology therefore include all of mankind. Before this technology can be implemented, it is important to thoroughly characterize the vaccine producing plants. In this report, we have characterized transgenic maize plants carrying a model edible vaccine called LT-B. We found that this vaccine accumulates in the starch granules of maize kernels. This is an important observation because a starch-encapsulated vaccine may be more effective when administered orally than a vaccine that accumulates in other ways.

Technical Abstract:
The B subunit of Escherichia coli heat labile enterotoxin (LT-B) is a potent oral immunogen, with potential for use as a vaccine and an adjuvant to co-administered vaccine. LT-B produced in plants was shown to be functional and immunogenic in animals and humans. Using immunogold labeling /electronmicroscopy and cell fractionation/western analysis, we show here that the LT-B protein accumulates in starch granules of transgenic maize kernels. LT-B accumulation in starch granules was observed when the protein was produced with its native bacterial signal peptide and the maize 27 kDa g-zein protein signal peptide. This represents the first case in which a bacterial protein is transported into the starch granules of a higher plant.